1. Field of the Invention
The present invention relates to a workpiece measuring apparatus for measuring at least one of a size and a shape of a workpiece.
2. Description of the Related Art
When a workpiece has been machined in a machine tool, the size or the shape of each portion of the machined workpiece is generally measured in the inspection process in order to check that the workpiece size obtained is suitable or to obtain feedback on the result of the machining. Especially in a turning or grinding process system, such as a grinding machine or a machining center, the size of the workpiece obtained by the machining process may change irregularly due to chipping of a tool, etc. and, therefore, the in-line or on-line inspection of a machined workpiece is often carried out.
In view of the recent remarkable progress of the machining speed of the machine tools, the throughput of a production line as a whole is dependent greatly on the throughput of the inspection process in the case where the in-line or on-line inspection is carried out as described above. Consequently, the workpiece measuring apparatus is required to measure the size or the shape of a workpiece rapidly.
On the other hand, a high dimensional accuracy has recently been required for a plurality of points of a machined part and, to meet this requirement, the workpiece measuring apparatus is required to have a high measurement accuracy for a plurality of points.
In order to meet these requirements, the conventional workpiece measuring apparatus is adapted to include a plurality of measuring gauges at fixed positions so that it can realize a high measurement accuracy and a high throughput by specializing each of the measuring gauges for the measurement of a specific portion of a workpiece having a specified shape and thereby limiting the measurable dimensional range to improve the measurement accuracy while, at the same time, making it possible to simultaneously measure different portions of a workpiece with a plurality of measuring gauges.
With the conventional workpiece measuring apparatus, however, the fact that the measuring gauges are fixedly arranged makes it difficult to change or add measurement positions in keeping with a change in the shape to which the workpiece is to be machined. Further, in view of the fact that the measurable dimensional range of each measuring gauge is limited, it is difficult even to follow the change in the size of the machined workpiece in versatile way. As a result, when the production line is changed, due to a change in the product design, a workpiece measuring apparatus is often required to be newly designed and developed.
Further, in the case where a recessed groove is formed in the outer peripheral surface of the workpiece together with the workpiece shape change, the conventional workpiece measuring apparatus poses the problem that the gauge head (i.e. the detector) of the measuring gauge is often trapped in the groove, thereby making it impossible to measure the outer peripheral size of the portion of the workpiece free of the groove. This is also the case with a workpiece having a hole of which the inner peripheral surface is formed with a recessed groove.
Also, the tool can be chipped off during the machining process, especially in the turning process, resulting in an excessively large machined workpiece. In the measuring gauge of a type in which the workpiece is measured by being arranged between two gauge heads, such an excessively large workpiece conveyed to the measurement position of the workpiece measuring apparatus would cause a problem of an interference with the two gauge heads and their resultant breakage.
Therefore, an object of the invention is to provide a workpiece measuring apparatus which can flexibly respond to a change in the production line due to a change in the product design.
Another object of the invention is to provide a workpiece measuring apparatus capable of measuring the size of that portion of the outer peripheral surface of a workpiece or that portion of the inner peripheral surface of a hole of a workpiece which is not formed with a recessed groove, even in the case where the workpiece or the hole thereof, as the case may be, is formed with such a recessed groove.
Still another object of the invention is to provide a workpiece measuring apparatus which can prevent gauge heads of a measuring gauge unit being broken even in the case where a workpiece larger than the measurable dimensional range of the measuring gauge unit is conveyed to a measurement position of the workpiece measuring apparatus.
According to the present invention, there is provided a workpiece measuring apparatus, for measuring at least one of a size and a shape of a workpiece, which includes:
a machine base;
a column mounted on the machine base and having a mounting mechanism on at least one of the side surfaces of the column;
a measuring gauge unit removably fixed at an arbitrary position on the mounting mechanism of the column; and
a conveying unit for conveying a machined workpiece to a measurement position where a measurement can be performed by the measuring gauge unit.
A plurality of measuring gauge units may be removably mounted independently of each other at arbitrary positions on the mounting mechanism.
Preferably, the mounting mechanism includes one or more guide grooves, and the measuring gauge unit includes one or more sliding elements, the sliding element adapted to slidably engage in the guide groove.
Preferably, the machine base includes a support portion and a base plate removably mounted on the top of the support portion, and a plurality of different mounting sites for mounting the column thereon are formed on the base plate, the column being removably fixed on the base plate.
In similar way, preferably, the measuring apparatus further includes an operation panel for an operator to control the operation of the measuring gauge unit and the conveying unit; the machine base includes a support portion and a base plate removably mounted on the top of the support portion; and a plurality of different mounting sites for mounting the operation panel thereon are formed on the base plate, the operation panel being removably fixed at one of the mounting sites on the base plate.
Preferably, the base plate is formed with an opening, and when an additional measuring gauge unit is disposed in the machine base, the additional measuring gauge unit can measure at least one of the shape and the size of the workpiece positioned above the base plate through the opening.
The workpiece measuring apparatus further includes an additional column formed with a mounting mechanism, the additional column being mounted on the column.
According to a preferred embodiment, when it is determined that at least one of a size of an outer peripheral surface of the workpiece and a size of an inner peripheral surface of a hole of the workpiece is out of a predetermined range, the workpiece is rotated and the measuring gauge unit thereafter measures at least one of the size of the peripheral surface of the workpiece and the size of the inner peripheral surface of the hole of the workpiece again.
In this case, for example, the conveying unit includes a guide unit mounted on the base plate and a workpiece mount rotatable about a rotational axis extending vertically and movable along the guide unit, and when a measured size of at least one of an outer peripheral surface of the workpiece and an inner peripheral surface of a hole is out of a predetermined range, the workpiece mount is rotated and the size of at least one of the outer peripheral surface of the workpiece and the inner peripheral surface of the hole of the workpiece is thereafter measured again.
According to another preferred embodiment, the measuring gauge unit includes an interference prevention plate, the interference prevention plate having a cutoff adapted to receive a workpiece smaller than a predetermined tolerable size when the workpiece moves to the measurement position, and when the workpiece larger than the tolerable size moves to the measurement position, the workpiece interferes with ends of an inlet of the cutoff thereby to stop the movement of the workpiece or to move the workpiece away from the measurement position.
In this case, the cutoff of the interference prevention plate is preferably at a position between gauge heads in open state in preparation for the measurement.
According to still another preferred embodiment, the measuring gauge unit includes a movable portion for holding gauge heads, a driving portion for supporting the movable portion through an elastic element and driving the movable portion and, a sensor for detecting the displacement of the movable portion with respect to the driving portion and, when the sensor detects the displacement of the movable portion with respect to the driving portion, the movement of the movable portion of the measuring gauge unit with respect to the workpiece is stopped or the workpiece and the measuring gauge unit are moved away from each other.
In the workpiece measuring apparatus according to the present invention, the measuring gauge unit can be removably mounted on the column at an arbitrary position of the mounting mechanism of the column. Therefore, even in the case where the machining shape of the workpiece is changed, the measurement position can be easily changed accordingly.
Further, since a plurality of measuring gauges can be mounted independently of each other at arbitrary positions of the mounting mechanism, the workpiece measuring apparatus can easily respond to the change in the number of the portions required for the size measurement.
If the mounting mechanism forms a guide groove and the sliding element of the measuring gauge unit slidably engages in the guide groove, the mounting position can be adjusted by sliding the measuring gauge unit along the guide groove.
If a plurality of different mounting sites are formed on the base plate mounted on the top of the machine base, the mounting position or the orientation of the machine base and hence the measurement position can be easily changed in response to the change of the production line. In similar way, the position of the operation panel can be easily changed.
If the base plate is formed with an opening, the shape or the size of the workpiece positioned above the base plate can be measured through the opening. Thus, if the change of the workpiece design arises the requirement for measuring the size of the lower part of the workpiece, it can be met.
Further, for example, in the case where a recessed groove is formed in an outer peripheral surface of a workpiece or an inner peripheral surface of a hole in a workpiece, the size of the workpiece in the recessed groove or the size of the hole of the workpiece can be, for example, measured by the measuring gauge unit. When it is determined that the measured size is out of a predetermined range, the size of that portion of the workpiece or the hole which is not formed with the recessed groove can be measured by rotating the workpiece.
If the measuring gauge unit is provided with an interference prevention plate, a workpiece larger than the tolerable size cannot reach the measurement position, and, therefore, the gauge heads of the measuring gauge unit are prevented from interfering with the workpiece and being broken.
In the case where the movable portion holding the gauge heads is supported on the driving portion through an elastic element, if the gauge head or the movable portion interferes with the workpiece and is subjected to a force more than a tolerable range by the workpiece, the elastic element contracts and the movable portion is displaced with respect to the driving portion. Therefore, by detecting this displacement of the movable portion with respect to the driving portion, it can be detected that the gauge head or the movable portion is subjected to an improper force by the workpiece. Thus, the workpiece can be separated from the movable portion and the gauge heads, before the movable portion or the gauge head are otherwise broken. This makes it possible to prevent the gauge head or the movable portion from interfering with the workpiece and being broken.